Clarify pathname docs, follow spec with fragments (#2448)

* Clarify pathname docs, follow spec with fragments

- Valid URLs must not contain a `#` within its fragment.
  https://github.com/MithrilJS/mithril.js/issues/2445
- Our docs were a little confusing and misleading - `m.pathname` isn't
  aware of URLs, just path names.
- Removed the relevant extension to `m.parseQueryString` required to
  support the hash parsing extension. Now we just shave it off and
  ignore it.
- Fix support for arbitrary prefixes, so prefixes like `?#` are
  handled correctly.
- Add a bunch of tests to cover various areas of confusion and unusual
  edge cases.

* Update with PR [skip ci]

docs/paths.md

@@ -123,7 +123,7 @@ m.route(document.body, "/edit/1", {
 })
 ```
 
-Note that query parameters are implicit - you don't need to name them to accept them. You can match based on an existing value, like in `"/edit?type=image"`, but you don't need to use `"/edit?type=:type"` to accept the value. In fact, Mithril would treat that as you trying to literally match against `m.route.param("type") === ":type"`. Or in summary, use `m.route.param("key")` to extract parameters - it simplifies things.
+Query parameters are implicitly consumed - you don't need to name them to accept them. You can match based on an existing value, like in `"/edit?type=image"`, but you don't need to use `"/edit?type=:type"` to accept the value. In fact, Mithril would treat that as you trying to literally match against `m.route.param("type") === ":type"`, so you probably don't want to do that. In short, use `m.route.param("key")` or route component attributes to read query parameters.
 
 ### Path normalization